Augmented reality (AR) viewing may be defined as a live view of a real-world environment whose elements are supplemented (e.g., augmented) by computer-generated sensory input such as sound, video, graphics, or haptic feedback. Virtual reality (VR) takes AR one step further and provides a fully immersive virtual world for the user. A head-mounted display (HMD), also sometimes referred to as a helmet-mounted display, is a device worn on the head or as part of a helmet that is able to project images in front of one or both eyes of a user. An HMD may be used for various applications including augmented reality or virtual reality simulations. HMDs are used in a variety of fields such as military, gaming, sporting, engineering, and training.